Cardiac intraventricular conduction delay results in mechanical dyssynchrony, dividing the heart into early and late contracting regions and worsening overall chamber function and mechanical efficiency. The clinical impact of this problem is large, affecting 15-30% of the millions of patients with dilated cardiomyopathy. Biventricular or left-ventricular stimulation can resynchronize the heart (cardiac resynchronization therapy, CRT), and this benefits cardiac function, clinical symptoms, and morbidity/mortality endpoints. However, many questions remain regarding optimal identification of responsive candidates and how to best implement and assess the therapy. There is virtually no existing data regarding basic molecular and cellular mechanisms by which dyssynchrony (and CRT) impact the failing or normal myocardium. Our Program Project aims to critically address this lack of knowledge. The proposed studies draw from our recent discoveries that marked molecular and electrophysiologic abnormalities are induced in the late-contracting lateral endocardium, and that mechanical/electrical dyssynchrony are far from synonymous. We developed a novel large animal model that combines cardiac failure with contractile dyssynchrony and can also examine either feature alone. The three projects in the Program are highly integrated making use of the common model and informing each other with respect to mechanisms and data interpretation. Project by Van Eyk focuses on molecular signaling affected by dyssynchrony and CRT, examining targeted pathways associated with hypertrophy/stress response, broader sub-proteomes, and gene-transcription using a custom-canine array. We also test the consequences of dyssynchrony on regional myocyte function. Project by Halperin focuses on electrophysiological abnormalities, utilizing optical mapping of myocardial wedge preparations to study transmural heterogeneity, and conducting electrophysiology and molecular analyses. Project by Tomaselli is performed at the chamber level and addresses central questions of CRT targeting, its implementation, and optimized dyssynchrony measurements. This Project utilizes our novel methods to combine 3-D magnetic resonance strain analysis with full chamber electrophysiology mapping. The Program will greatly expand our understanding of dyssynchrony and CRT providing important new and clinically relevant information. More broadly, this research should yield fundamental new insights into myocardial stress-signaling and heart failure pathophysiology.